What are the functions of MAVTVPCA on Canon 500D camera?

First of all, I suggest you read the instructions carefully. This is your first time to learn photography.

M is manual mode, shutter aperture, iso color mode and white balance focusing mode, which you need to set manually.

Av is aperture priority. You just need to set the aperture metering mode. The shutter is set by the camera according to your aperture value.

Television is shutter priority, that is, you set the shutter speed yourself, and the aperture is set by the camera.

P is the program exposure. You just need to set iso or something. The aperture shutter camera will set itself according to the metering value.

Ca is a creative mode, basically a novice mode. You have to choose the shooting effect, such as the background light and dark, fuzzy or clear, and then the camera is responsible for setting the shooting parameters to achieve the effect you set.